Downhole apparatus

ABSTRACT

Downhole apparatus is described having a tubular main body and at least one flow channel formed on the body. The channel has at least one non-uniform dimension. A flow guide is located adjacent an end of the channel, and the flow guide and the channel together define a flow path for flow of a downhole medium along the body. The downhole apparatus may for example be a casing reamer shoe, a drill pipe, or a motor sleeve.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 60/661,558, filed Mar. 14, 2005, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to downhole apparatus for use in the oil and gas exploration and production industry, such as apparatus for use in the drilling and completion of a wellbore of an oil or gas well and in subsequent intervention procedures. In particular, but not exclusively, the present invention relates to drill pipe, a centraliser, a stabiliser, a downhole tubing shoe, a reamer, a sleeve or housing of a downhole tool or a tool sub, and/or a cleaning tool.

2. Background of the Related Art

A number of different types of downhole tools and equipment are used in the oil and gas exploration and production industry during the drilling of a wellbore, lining of the drilled bore with a metal casing/liner, and in the subsequent completion of the well to gain access to subterranean hydrocarbon bearing rock formations.

These tools and equipment include, for example, drill strings used in the drilling of a wellbore; stabilisers and centralisers used for centralising equipment in a borehole or downhole tubing; reamers and other cutting tools used for reaming a drilled borehole wall; and cleaning tools used for cleaning downhole tubing preparatory to completion of a well or in an intervention procedure.

In more detail, an oil or gas well is drilled using a drill string which typically comprises lengths of drill tubing sections coupled together end-to-end, with a drill bit at a lower end for performing the task of boring the rock formation. Drill collars, which are relatively heavyweight drill pipe sections, are provided above the bit to assist both in keeping the direction of drilling consistent and to take up much of the loading in the string resulting from the drilling operation. The drill string is typically rotated from surface by a rotary table on a drilling rig, or by a dedicated fluid-driven downhole motor, which drives the drill bit to form a well borehole.

During drilling, drilling fluid such as a drilling ‘mud’ is pumped into the wellbore through the drill string, exiting through ports in the drill bit and returning to surface along an annulus formed between the drill string and the borehole wall. The drilling fluid serves a number of purposes including cooling the drill bit, and carrying drill cuttings to surface.

A number of factors affect the transmission of torque to the bit through the drill string, including vibration of the drill bit; differential sticking due to penetration of clay rich formations; effective removal of cuttings and drilling fluid; and surface friction.

Different downhole tools and aids are typically employed to assist during a drilling operation, and bottomhole assemblies may include stabilisers that provide a stand-off from the wellbore walls, the outer surface of the stabiliser providing a snug clearance fit to the wellbore walls. These help to keep the drill pipe and heavyweight drill collar spaced from the wellbore wall, reducing friction and maintaining the drill bit in the correct position within the wellbore, thereby and thus helping to maintain torque on the bit.

Known drill string stabilisers are typically cylindrical tubular elements which are fitted around the drill pipe or provided integrally with the pipe, and often include grooves to allow fluid to pass relatively unrestricted upwards through the well borehole. Some known stabilisers have helical groove channels extending around the body of the pipe, which help to remove fluid and debris away from the drill bit or a drill shoe and along the wellbore annulus to surface.

In a similar fashion, drill collars of a bottomhole assembly may carry integral stabiliser arrangements of a similar structure, or a stabiliser arrangement of this type may be provided above the drill bit, for a similar purpose of helping to remove fluid and debris away from the bit or shoe to surface.

Grooved stabiliser elements are also used during reaming, which is either a secondary drilling process for re-entering an existing wellbore, for example for enlarging the wellbore diameter, or for ensuring a drilled borehole is of a desired diameter.

Before a wellbore can be completed to gain access to well fluids, the well borehole is usually lined with a metal casing, which is cemented in place to prevent the wellbore wall from collapsing. The casing typically carries a number of casing centralisers which centralise the casing in the borehole, and ensure that an annulus around the casing outer surface is maintained, to assist in subsequent cementation. Cement is then pumped down the casing and into the annulus, carrying residual drilling fluid ahead of the cement to surface, and it is important that the cement is adequately circulated and distributed around the casing. It is therefore important that casing centralisers allow adequate flow of cement along the annulus.

Many casing centralisers are of a type including bowsprings that act against the borehole wall to centralise the casing. However, in a similar manner as for stabilisers, some known centralisers are provided as tubular elements with channels for assisting upward flow of drill fluid and cement, the channels enhancing turbulence of the fluid flowing up the annulus between the casing and the borehole wall.

Similar considerations of effectively removing fluid and cuttings from the well bore are pertinent to well cleaning operations that may be performed subsequent to casing the borehole and prior to completion of the well.

Although prior art systems have addressed some important issues there remain a number of significant disadvantages with the proposed systems. One particular problem during rotary drilling is differential sticking, where the drill pipe sticks to the wellbore wall. This is particularly common when drilling through clay rich formations, and occurs when the wellbore pressure is greater than the drilled formation pressure. Formations of this type also cause ‘balling’ of debris, where solids such as clays stick to the bit and components of the drill string due to fluid clay interaction and pressure.

International Patent Publication No. WO 9105936 (Weatherford US, Inc.) discloses a centraliser, stabiliser, or pipe protector with a fluted tubular cylindrical outer surface that directs and channels fluid flow upwards through the wellbore. The tool is designed such that the diameter of the outer surface of the tool varies in order to create regions that produce a nozzle effect on the flow of fluid passed over the tool in the annular space.

The channels are generally elongate in the axial cylindrical direction and may be off-set to the axis, additionally creating a helical path for the fluid. Ribs protrude from the outer surface such that they perform a centralising or stabilising function, creating an annular space between the tubular member and the wellbore wall. The width of the ribs may also vary in order to enhance the nozzle effect on the fluid.

Another centraliser is disclosed in U.S. Pat. No. 5,881,810 (Weatherford/Lamb, Inc.), which comprises two annular metal members located around a pipe and rectilinear parallel slats attached to the members at an angle to the axis of the wellbore.

A drill tool protector is disclosed in UK Patent Publication No. 2288198 (Hydril), which has a channelled outer surface where two distinct flow paths for fluid are provided by diamond shaped protruding elements on the exterior cylindrical and tubular surface of the protector.

It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided downhole apparatus comprising:

-   a tubular main body; -   at least one flow channel, the channel extending at least part way     along a length of the body and at least one dimension of the channel     being non-uniform; and -   at least one flow guide located adjacent an end of the channel, the     flow guide and the channel together defining a flow path for flow of     a downhole medium along the body.

The apparatus has a variety of uses in the downhole environment, and is typically coupled to downhole tubing, or provided as part of a downhole tubing string or tool, adapted to be located downhole. In use, the apparatus may be located in an open hole environment (for example, in a drilled borehole), or within existing downhole tubing such as a casing or liner, and downhole medium present in the borehole/tubing may flow past the body along the flow channel.

It will be understood that the downhole medium is capable of flow and typically comprises a solids-laden fluids, such as drilling mud (which is utilised, inter alia, to carry drill cuttings to surface); a viscous fluid such as cement; completion fluids; well fluids or the like, or a mixture thereof. It will also be understood that references herein to at least one dimension of the channel being non-uniform are to said dimension having at least one variation along the length of the channel. The relevant dimensions of the channel may include, for example, one or more of a width, depth and/or length of the channel.

By providing downhole apparatus having a flow channel where at least one dimension of the channel is non-uniform, flow characteristics of a downhole medium flowing through the channel (such as velocity, pressure and turbidity) may vary along the length of the channel. This may promote turbulent flow resulting in thorough mixing of constituents of the downhole medium, and/or scouring of surfaces of the channel to prevent adhesion of materials to the channel walls. This may thereby assist in preventing blockage of the channel by, for example, solids such as drill cuttings, mud residues and the like present in the downhole medium. In preferred embodiments, the flow channel may define at least one nozzle, restriction or the like tending to cause an increase in velocity of a downhole medium flowing through the channel, assisting in preventing blockage of the channel by solids in the medium, by jetting the medium through the channel. Furthermore, provision of restrictions of this type may assist clearing of any blockages that may occur, by creating a piston-effect, in use. This is because any blockage will result in an increase in pressure of the medium behind the blockage, tending to urge the blocked solids through the restriction to clear the channel.

The apparatus may be dimensioned to be a close fit with a tubing in which the apparatus is located. Where the apparatus is located in open hole, the apparatus may also be dimensioned to be a close fit with the borehole wall, or indeed an interference fit, such that the apparatus may serve for reaming the borehole to a desired diameter. This may be achieved by providing the apparatus with at least one cutting and/or reaming surface, blade or the like. The channel may therefore be adapted to be bound on one side by an internal wall of tubing or the borehole, such that all or most of the flow of downhole medium past the body is directed along the channel.

The apparatus may be provided as an integral part of a tool or tubing string, or as a separate component adapted to be coupled to tubing of a tool string or sections of a tubing string such as a length of casing.

The apparatus may be a centraliser for centralising a body such as a tubing or tool string within an open hole or within existing downhole tubing such as a casing or liner. For example, during drilling of an oil or gas well, it is necessary to line a drilled borehole with a metal casing, and the apparatus may be a centraliser for centralising such a casing in the drilled borehole prior to cementation. In a variation, the apparatus may be a stabiliser, which may be utilised, for example, for centralising and stabilising a drill string in an open hole during drilling of a borehole. In a further variation, the centraliser/stabiliser may be provided on or as part of a drill collar or other tubing section of a drill string.

Alternatively, the apparatus may form part of a shoe such as a casing shoe or a drill shoe. A shoe is the lowermost section of a tubing string in a borehole, thus a casing shoe is the lowermost section of a casing string in a borehole. The casing shoe may comprise a drillable lower end, which may be shaped to guide the casing into the borehole, and which may be a jetting nozzle having a jetting port(s) for jetting a fluid into the borehole, to assist passage of the casing. A drill shoe is the lowermost section of a drill string, and may carry a drill bit or the like, or a jetting nozzle; a jetting nozzle may be utilised depending upon the particular rock formation to be drilled, and may be more suitable for relatively soft formations. In a particular embodiment, the apparatus may be a casing shoe reamer which may assist passage of a casing string into a drilled bore, and includes reaming surfaces, such as reaming blades, for reaming the borehole wall. In a similar fashion, the apparatus may alternatively be a drill shoe reamer.

Alternatively, the apparatus may be a sleeve or housing of a downhole tool such as a downhole motor and may serve for centralising/supporting the tool within a borehole/downhole tubing. It will be understood that the sleeve may form an outer housing or sleeve of the tool, or may be provided as a separate component adapted to be coupled to the tool. Thus the apparatus may form an outer sleeve or housing of a main part of a motor, or may be provided as a sub adapted to be coupled to a main part of a motor. It will be understood that downhole motors include downhole fluid driven turbines and motors such as Positive Displacement Motors (PDMs).

In a further alternative, the apparatus may be a cleaning tool for cleaning a borehole, and may include at least one of a cleaning or abrading blade, brush, scraper, wiper or the like for cleaning the wall of a downhole tubing.

Preferably, the apparatus comprises a plurality of ribs, arms, shoulders or the like, each rib upstanding or extending outwardly from an outer surface of the body, and extending at least part way along a length of the body. The ribs may be spaced around a circumference of the main body, and the channel may be defined between an adjacent pair of ribs. The apparatus may therefore comprise a plurality of channels, and each channel may be defined or bound by an outer surface of the body and side walls of the adjacent ribs. It will be understood that the apparatus may therefore comprise a plurality of flow paths for flow of fluid past the body. In alternative embodiments, the channel may be formed in or by the main body and may therefore be formed in an outer surface of the body.

The ribs may have a respective rib main axis, and the ribs may be disposed on the body such that the rib main axes are substantially parallel with one another. Alternatively, at least one of the ribs may be disposed such that the respective rib axis is non-parallel to the rib axis of the other rib, or one or more of the other ribs.

Preferably, the ribs are adapted to be coupled to the main body, and may be releasably couplable to the main body to facilitate removal for maintenance and/or replacement. In a variation, part or parts of the ribs adapted to contact the borehole/tubing wall may be releasably couplable to a main portion of the rib, for maintenance and/or replacement of said rib part. Alternatively, the ribs may be may be provided as integral parts of the main body.

The apparatus may be adapted to be translated relative to the borehole/downhole tubing with the body in sliding contact with the borehole/tubing wall. To facilitate this movement, the main axis of each rib, and thus of corresponding axes of the channels, may be disposed substantially parallel to a longitudinal axis of the body. Such an arrangement may reduce or avoid generation of a reaction torque in the body due to flow of downhole medium through the channel when the body is translated relative to the borehole/tubing.

Alternatively, the main axis of each rib and thus corresponding axes of the channels may be disposed non-parallel to a longitudinal axis of the body, that is, inclined relative to the body axis. For example, in embodiments of the invention, the ribs may be helically oriented and thus may extend in a helical direction around the body. This may be of particular utility where it is desired, for example, to promote turbulence in the downhole medium, which may facilitate cleaning and/or transportation of the medium, in particular any entrained solids, to surface.

The channel may define a corresponding channel axis and the flow guide may be located on or parallel to the channel axis and may be spaced axially along the body relative to the channel. Preferably, the flow guide is located such that downhole medium flowing out of the channel impinges on the flow guide (which may assist in preventing blockage of the channel by breaking up and mixing the flow of the downhole medium and thus of the downhole medium constituents), and/or so as to direct downhole medium around the flow guide and into the channel. It will be understood that the flow guide directs the medium flowing away from or into the channel depending upon the direction of flow of fluid relative to the body.

The flow guide may have a first (axially) inward end, relative to the channel, and a second (axially) outward end, relative to the channel. Thus the first end may face inwardly towards the channel and the second end may face outwardly. The first end may define a surface facing the channel, the surface having a leading edge or portion and at least two lateral surface portions which extend away from the leading edge and which are inclined relative to the channel axis. For example, the first, inward end of the flow guide may be generally triangular and may be in the shape of an arrow head. The flow guide may therefore form two flow path portions extending around the flow guide for directing medium flowing away from the channel, and/or for directing medium into the channel; it will again be understood that the flow guide directs the medium flowing away from or into the channel depending upon the direction of flow of fluid relative to the body. The flow path portions may be defined between the first end of the flow guide and an adjacent end or area of the main body or ribs forming the channel.

Preferably also, the channel has first and second axial ends, and the apparatus comprises two flow guides associated with the channel, one located adjacent to the first end of the channel and the other located adjacent the second end. In this fashion, depending upon the direction of flow of fluid relative to the apparatus, one of the flow guides may serve for directing fluid into the channel and the other flow guide may serve for directing fluid flowing out of the channel. Where the apparatus comprises a plurality of channels, the apparatus may comprise at least two flow guides associated with each channel.

The channel width and/or depth may be non-uniform along a length of the channel. The channel may define at least one flow restriction where the width and/or depth of the channel is reduced compared to an adjacent portion or area of the channel. This may define a nozzle which may serve, in use, for increasing a velocity of medium flowing therethrough. In a preferred embodiment of the invention, the channel defines two such restrictions, one at or adjacent each end of the channel, with a relatively unrestricted portion (for example, a portion or area of greater width/depth) at a location between the restrictions in a direction along the length of the channel. In this fashion, medium entering the channel may be accelerated through a nozzle (which may promote turbulent flow) and may then enter the area of greater width, where it may slow and mix before being accelerated and jetted through the second restriction (which may again promote turbulent flow). This may successively cause, for example, turbulent, laminar and turbulent flow of the downhole medium.

In alternative embodiments, ends of the channel are of greater width relative to a portion or area at a location between the ends in a direction along the length of the channel. However, any other suitable desired arrangement/number of restrictions may be provided in the channel by appropriate shaping thereof.

It will be understood that the channel width may be varied according to a spacing between side walls or edges of the channel, whilst the depth (in a radial or outward direction relative to the main body) may be varied according to a wall thickness of the main body and/or depth of the ribs.

Where the channel is defined between adjacent ribs, the width of the channel may be varied according to and determined by the shape/dimensions of the ribs. Thus the restrictions in the flow channel may be defined by areas of the ribs of relatively greater width. In preferred embodiments, each rib may have first and second ends of greater width relative to a portion of the rib at a location between said ends. For example, each rib may be elongate and may have ends defining lobes or the like and with a section extending between the lobes of reduced width. Side walls of the ribs may be curved, to define a smooth transition between areas of the rib of larger and smaller width, although in alternative embodiments, it may be desired to provide a sharp transition between said areas of the rib if deemed appropriate in view of desired flow characteristics of medium flowing through the channels.

The ribs may define an outer surface adapted to abut an inner wall of a borehole or a tubing in which the apparatus is located, and a diameter described by the ribs may thus be greater than an outer diameter of the main body. The ribs may be shaped such that the ribs are adapted to abut said wall over a majority, for example, 75% or more, optionally 90% or more, of an internal circumference of the wall at a selected location or locations along the length thereof. This location may correspond to portions of the ribs of greater width. This may, in use, provide improved stability when compared to known apparatus such as prior centralisers/stabilisers. These locations may be spaced apart along the length of the ribs so as to optimise stability of the apparatus, in use. Furthermore, this arrangement of the ribs may facilitate flexing of the apparatus in use, the main body flexing in regions of the body where the ribs are of reduced width.

The apparatus may comprise a plurality of flow guides spaced around a circumference of the body, adjacent flow guides defining part of a flow path. Adjacent flow guides may define a circumferential opening therebetween, which may define an inlet and/or outlet of one or more flow path. The openings may be circumferentially spaced or staggered relative to axes of the channels. This may define a tortuous flow path for flow of the downhole medium around the flow guide and through the channel and thus across the body, improving mixing and reducing the likelihood of balling or adhesion of solids in the medium on the apparatus and in particular on the channel walls.

Preferably, the apparatus comprises at least one cutting, abrading or reaming surface for abrading the borehole/tubing wall. The rib outer surfaces may each define or carry abrasive particles, such as Tungsten-Carbide grit, and/or the ribs may define cutting surfaces, for example, edges of the ribs may define cutting blades. The flow guide may have an outer surface carrying abrasive particles, and/or edges of the flow guide may define cutting surfaces. The flow guide may be shaped to define a plurality of cutting surfaces, and one or both of the first and second ends of the flow guide may define a cutting surface. In a particular, preferred embodiment, where the apparatus comprises two flow guides associated with each channel, the second end of one or both of the flow guides may define a relatively aggressive cutting surface, whilst the first end of one or both of the flow guides may define a less aggressive cutting surface. In particular, the second end of the flow guide provided, in use, lowermost on the apparatus may define a relatively aggressive cutting surface. This second end of the lowermost flow guide may face downhole, in use, during running-in of the apparatus. This has a particular utility where the apparatus is a drill shoe or the like, as the aggressive cutting surface forms a reamer that follows a lower drill bit and ensures the drilled borehole is of a desired diameter.

According to a second aspect of the present invention, there is provided downhole apparatus comprising:

-   a tubular main body; and -   a plurality of elongate ribs upstanding from an outer surface of the     main body and extending at least part way along a length thereof,     adjacent pairs of ribs defining a flow channel therebetween for flow     of a downhole medium along the body; -   wherein the ribs are shaped such that at least one dimension of each     channel is non-uniform and such that respective axes of the channels     are disposed substantially parallel to a longitudinal axis of the     body.

According to a third aspect of the present invention, there is provided downhole apparatus comprising:

-   a tubular main body; -   at least one flow channel for flow of a downhole medium along the     body, the flow channel having a respective flow channel main axis,     the channel extending at least part way along a length of the body     and at least one dimension of the channel being non-uniform; and -   at least one flow guide located adjacent an end of the channel and     disposed on the flow channel axis.

According to a fourth aspect of the present invention, there is provided a downhole tubing shoe comprising:

-   a tubular main body; -   at least one flow channel for flow of a downhole medium along the     body, the channel extending at least part way along a length of the     body, at least one dimension of the channel being non-uniform, and     an axis of the channel being disposed substantially parallel to a     longitudinal axis of the body.

The shoe may be a casing shoe or a drill shoe. The apparatus may define a reamer, thus the apparatus may be a reamer shoe, such as a casing shoe reamer or a drill shoe reamer.

According to a fifth aspect of the present invention, there is provided a sleeve for a downhole motor, the sleeve comprising:

-   a tubular main body; -   at least one flow channel for flow of a downhole medium along the     body, the channel extending at least part way along a length of the     body, at least one dimension of the channel being non-uniform, and     an axis of the channel being disposed substantially parallel to a     longitudinal axis of the body.

According to a sixth aspect of the present invention, there is provided a downhole cleaning tool, the cleaning tool comprising:

-   a tubular main body; -   at least one flow channel for flow of a downhole medium along the     body, the channel extending at least part way along a length of the     body, at least one dimension of the channel being non-uniform, and     an axis of the channel being disposed substantially parallel to a     longitudinal axis of the body.

According to a seventh aspect of the present invention, there is provided a centraliser comprising:

-   a tubular main body; -   a plurality of elongate ribs upstanding from an outer surface of the     main body and extending at least part way along a length thereof,     adjacent pairs of ribs defining a flow channel therebetween, the     ribs shaped such that at least one dimension of each channel is     non-uniform and such that respective axes of the channels are     disposed substantially parallel to a longitudinal axis of the body;     and -   at least one flow guide upstanding from the outer surface of the     main body, the flow guide located adjacent an end of the channel     such that the flow guide and the channel together define a flow path     for flow of a downhole medium along the body.

According to an eighth aspect of the present invention, there is provided a stabiliser having the features of the seventh aspect of the invention defined above.

Further features of the second to eighth aspects are defined above in relation to the first aspect of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of downhole apparatus in accordance with a preferred embodiment of the present invention;

FIG. 2 is a repeated view of the downhole apparatus of FIG. 1 showing certain additional features;

FIGS. 3 and 4 are views of the downhole apparatus of FIG. 1 viewing in the direction of the arrows B and C of FIG. 1, respectively;

FIG. 5 is a view of part of a drill string in accordance with an alternative embodiment of the invention, shown during drilling of a borehole, the drill string including downhole apparatus similar to the apparatus of FIG. 1;

FIG. 6 is an enlarged, perspective view of part of the drill string of FIG. 5;

FIG. 7 is a perspective view of a drill shoe in accordance with a further alternative embodiment of the invention, including downhole apparatus similar to the apparatus of FIG. 1;

FIG. 8 is a perspective view of a casing shoe in accordance with a further alternative embodiment of the invention, including downhole apparatus similar to the apparatus of FIG. 1;

FIGS. 9 and 10 are views of the downhole apparatus of FIG. 8 viewing in the direction of the arrows G and H of FIG. 8, respectively;

FIG. 11 is a perspective view of a cleaning tool in accordance with a further alternative embodiment of the invention, including downhole apparatus similar to the apparatus of FIG. 1;

FIGS. 12 and 13 are views of the cleaning tool of FIG. 11 viewing in the direction of the arrows I and J of FIG. 11, respectively;

FIG. 14 is a further perspective view of the cleaning tool of FIG. 11; and

FIGS. 15 and 16 are views of the cleaning tool shown in FIG. 14 viewing in the direction of the arrows K and L of FIG. 14, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention overcomes many of the prior art problems associated with multi-function downhole apparatus. The advantages, and other features of the system disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present invention. Turning firstly to FIG. 1, there is shown a perspective view of a downhole apparatus in accordance with a preferred embodiment of the present invention, the downhole apparatus indicated generally by reference numeral 10. As will be described in more detail below, the downhole apparatus 10 may take the form of one of a number of different types of downhole tools or equipment. However, in general terms, the downhole apparatus 10 comprises a tubular main body 12; at least one flow channel 14, the channel 14 extending at least part-way along a length of the body 12 and at least one dimension of the channel 14 being non-uniform; and at least one flow guide 16 located adjacent to an end 18 of the channel 14, the flow guide 16 and the channel 14 together defining a flow path A for flow of a downhole medium along the body 12.

The apparatus 10 serves for promoting improved fluid flow along an annulus defined between the body 12 and the wall of a well borehole or of a tubing in which the apparatus is located. It will therefore be understood that the apparatus 10 may be located in open hole, that is within a drilled borehole of an oil or gas well; within tubing previously located in a borehole such as a casing or liner; or indeed within other tubing such as a tool string. The apparatus 10 therefore has a wide range of potential uses in the downhole environment.

There follows a more detailed description of the structure of the downhole apparatus 10, followed by descriptions of particular tools or equipment incorporating or comprising the apparatus 10.

Turning now also to FIG. 2, there is shown a further view of the downhole apparatus 10 of FIG. 1. FIGS. 3 and 4 are also referred to, which are views of the downhole apparatus 10 taken in the direction of the arrows B and C of FIG. 1.

The tubular main body 12 includes a plurality, in the illustrated embodiment, three elongate ribs located at 120 degree spacings around a circumference of the body 12, and two such adjacent ribs 20 a, 20 b are shown in the drawings. A flow channel 14 is defined between each adjacent pair of the ribs 20, and one such channel 14 b is shown and is defined between the ribs 20 a, 20 b. The channel 14 b is bound by respective side walls 22 a, 22 b of the ribs 20 a, 20 b and an outer surface 24 of the main body 12.

The ribs 20 a, 20 b are each shaped such that a circumferential width of the channel 14 defined between the rib side walls 22 a, 22 b varies along a length of the channel 14. In particular, each of the ribs 20 a, 20 b have respective first and second ends 26 and 28 of a greater circumferential width relative to a central portion 30, and the side walls 22 a, 22 b are curved along the length of the channel 14.

The respective ends 26 a, 26 b and 28 a, 28 b of the ribs 20 a, 20 b define flow restrictions in the form of nozzles 32, 34 in the channel 14, which present a restriction to fluid flow, accelerating downhole medium as it enters and exits the channel 14. It will be understood that, in the downhole environment, the downhole medium may typically comprise drilling fluid such as a drilling mud, cement, well fluids, completion fluids and the like or indeed a mixture thereof. These fluids typically carry entrained solids, for example, drilling mud is a mixture of a number of different fluids and abrasive solid particles and, in use, carries solid drill cuttings to surface.

In use, a downhole medium such as drilling mud entering the channel 14 is accelerated through the restriction 32, and then slows as it enters a central channel region 36, before being accelerated and jetted through the restriction 34. In this fashion, the drilling mud may transition from laminar flow during approach to the entrance of the channel 14 defining the restriction 32, transitioning to turbulent flow during passage through the restriction 32. The fluid may then return to laminar flow as it enters and travels along the central region 36, before again transitioning to turbulent flow during passage through the flow restriction 34. This achieves a thorough mixing of the drilling mud, drill cuttings and the like, which assists in preventing blockage of the channel 14, for example, by adhesion of solids in the drilling mud to the walls of the channel 14. In particular, balling of clay residues is prevented or substantially reduced.

The apparatus 10 also includes a set 38 of flow guides 16 a, 16 b, 16 c and a further set 40 of flow guides 42 a, 42 b and 42 c, as shown in FIG. 2. The three flow channels 14 are spaced around the circumference of the main body 12 and two of the channels 14 a, 14 b are shown in FIG. 4. Each of the channels 14 includes a respective pair of flow guides and, considering FIG. 2, the channel 14 b includes a flow guide 16 b adjacent the first end and a flow guide 42 b adjacent a second end 44.

When the apparatus 10 is run into a borehole or downhole tubing, fluid flows upwardly along an annulus between a tool or tubing string (not shown) supporting the apparatus 10, in the direction of the arrow D (FIG. 2). The fluid is directed by the flow guide 16 b along the flow path A (FIG. 1) into the channel 14, flowing out of the second end 44 and directed around the flow guide 42 b. The flow guides 16 b and 42 b thus serve for directing fluid into the channel 14 b, and for directing fluid flowing out of the channel 14 b uphole. However, it will be appreciated that fluid flow in an opposite direction E will be directed into the channel 14 by the flow guide 42 b, whilst the fluid flowing out of the channel 14 b will be directed by the flow guide 16 b.

The flow guides 16 b, 42 b are each located on and thus aligned with an axis 46 of the channel 14 b. Each of the flow guides 16 b, 42 b are shaped to define respective first and second ends 47, 49 as shown in FIG. 1. The first end 47 of each guide 16 b, 42 b forms a surface that faces axially inwardly, towards the channel 14 b, whilst the second ends 49 face axially outwardly. The surfaces 47 include a leading edge or point 48 that is aligned with the channel axis 46, and lateral surface portions 50, 52 that extend away from the leading edge and are inclined relative to the channel axis 46. Accordingly, each flow guide 16 b, 42 b is generally triangular and in particular is arrow-shaped.

In use, fluid flowing in direction D is jetted from the nozzle 34, and impinges upon the leading edge 48, which splits the fluid flow, thoroughly mixing and disrupting the flow of the fluid, to prevent adhesion of solid particles, and directs the fluid along the lateral surface portions 50, 52 and thus away from the body 12. This impinging of the fluid on the leading edge 48 also serves to split or ‘munch’ masses of balled or collected solids in the fluid stream, thereby enhancing fluid flow across the body 12. The restrictions/nozzles 32, 34 also assist in clearing any blockages that may occur, by creating a piston-effect, in use. This is because any blockage will result in an increase in pressure of the medium behind the blockage, tending to urge the blocked solids through the restriction to clear the channel. This effect may be enhanced in the event of a blockage by repeated advancement and retraction of the apparatus 10 up and down the borehole/tubing wall, to create a pumping effect on the blocked materials.

Adjacent pairs of the flow guides 16 in the first flow guide set 38 define circumferential openings therebetween, and two such openings are shown in FIG. 1 and given the reference numerals 54, 56. The flow guides 16 are shaped such that the openings 54, 56 also define a flow restriction or nozzle, jetting fluid through the nozzle where it impinges upon an end surface 58 of the rib 20 b. In a similar fashion to the flow guide 42 b, this enhances mixing of the constituents of the downhole medium. From there, the fluid is directed, for example, along the flow path A between the flow guide 16 b lateral surface portion 52 and the rib end surface 58, and thus into the nozzle 32.

It will therefore be understood that the arrangement of the first set of flow guides 38, the various channels 14 defined by the ribs 20, and the second set of flow guides 42 define a number of flow paths for flow of fluid across the main body 12 of the apparatus 10. These various flow paths provide an efficient mixing of constituents of the downhole medium, and splitting of any balled or accumulated solids in the flowing fluid, thereby preventing blockage of the flow paths and in particular the channels 14, in use.

The shape and arrangement of the ribs 20 to define the axially spaced nozzles 32, 34 additionally improves stability of the apparatus 10, in use. This is because the relatively wider sections of the ribs 20 forming the nozzles 32, 34 provide a relatively large circumferential contact area with a borehole/tubing wall in the locations of the nozzles. Indeed, the ribs 20 may be dimensioned such that the ribs abut the wall over a majority, for example, 75% or more, optionally 90% or more, of an internal circumference of the wall, at the locations of the nozzles 32, 34. This provides the additional advantage that the apparatus 10 is flexible, in particular in the region 36 where the ribs 20 are of relatively reduced width.

The apparatus 10 additionally defines a number of cutting or abrading surfaces, for reaming a borehole, or for cleaning an inner surface of tubing in which the apparatus is located. In more detail, the end 49 of each flow guide 16 typically forms a relatively aggressive cleaning blade or scraper for reaming/cleaning during passage of the apparatus downhole. In a similar fashion, the end 49 of each flow guide 42 define less aggressive blades or scrapers, to provide a reaming/cleaning function when the apparatus is translated uphole. Also, each of the ends 47 of the guides 16 and 42, and the edges of the rib side walls 22, may define blades or scrapers, for providing a rotary reaming/cleaning function. Also, ends of the ribs 20 may define similar such blades. Furthermore, radially outer surfaces of the apparatus 10, such as outer surfaces of the ribs 20 and guides 16, 42 may define or include abrasive particles, and may, for example, be coated with Tungsten-Carbide grit.

Each of the ribs 20 have respective rib axes 37 (FIG. 3), and the ribs 20 are each located on the body 12 such that the rib axes 37 are disposed parallel to a longitudinal axis 39 (FIG. 4) of the body 12. Accordingly each of the corresponding channel axes 46 are similarly disposed parallel to the body axis 39. Locating the ribs 20 and channels 14 in this fashion improves sliding motion of the apparatus 10 relative to a wall of the borehole/ tubing in use, by reducing or avoid generation of a reaction torque in the body 12 due to flow through the channel 14 when the body is translated relative to the borehole/tubing. The shape of the ribs 20 may also be such that the apparatus 10 provides improved contact with a borehole/tubing wall (that is, a greater surface area) when compared to prior apparatus.

Also, if desired, a wall thickness of the main body 12 may be varied along a length thereof, or in selected locations, to provide variations in the depth of the one or more of the channels 14, creating a similar nozzle effect to the restrictions 32, 34.

There now follows a detailed description of various downhole tools or tubing strings based upon the apparatus 10 of FIGS. 1-4.

Firstly, the apparatus 10 described above may form a sleeve or housing of a downhole tool, in particular, of a downhole motor such as a turbine or PDM. In a variation, the apparatus 10 may form a separate body or sub coupled to such a downhole motor. This may provide improved or enhanced flow of downhole medium, such as drilling fluids and entrained cuttings, along an annulus defined between a drill string carrying the motor and the borehole/tubing wall to surface.

FIG. 5 is a view of part of a drill string 60 shown during drilling of a borehole 62. The drill string is comprised of a number of tubing sections 63 coupled together end-to-end with a bottomhole assembly 64 provided lowermost in the string. The assembly 64 includes two or more tubing sections 66, 68 coupled together, the tubing section 68 being coupled in-turn to a number of relatively heavy drill collars, one of which is shown and indicated by reference numeral 70. The drill collars 70 are provided above a drill bit (not shown) which is lowermost in the assembly, which is used for drilling the borehole 62. Also, the tubing sections 66, 68 each carry a respective stabiliser 110, 210, each of which is identical in structure and operation to the apparatus 10 of FIGS. 1-4, and the stabiliser 110 is shown in more detail in the enlarged perspective view of FIG. 6. Like components of the stabilisers 110, 210 (and indeed of further tools/equipment that will be described below) with the apparatus 10 of FIGS. 1 to 4 share the same reference numerals incremented by 100, 200 etc.

In use, during drilling of the borehole 62, drilling mud is pumped down through a bore 72 of the drill string 60, exiting through nozzles or jetting ports in the drill bit, thereby cooling the bit and carrying drill cuttings to surface along an annulus 74 defined between an outer surface of the string 60 and an inner wall 76 of the borehole 62.

The stabilisers 110, 210 each serve to stabilise and centralise the drill string 60 within the borehole 62 and to assist in passage of drilling fluid and drill cuttings to surface, as described above. Furthermore, the reaming surfaces and blades of the stabilisers 110, 210 ream the borehole wall 76, to ensure that the borehole is of a desired diameter for subsequent operations including installation of a borehole casing.

Turning now to FIG. 7, there is shown a perspective view of a drill shoe 80 including a stabiliser 310 of similar structure and operation to the apparatus 10 shown in FIGS. 1-4. The stabiliser 310 is particularly suited for drilling a borehole in relatively soft formations, for example, clay based formations, and includes a drillable jetting nozzle 82 provided lowermost on the drill shoe 310. In use, drilling fluid flows down through an internal bore of the assembly 80, and is jetted in the direction F out of ports in the jetting nozzle 82, one of which is shown in FIG. 7 and given the reference numeral 84.

In a similar fashion to the stabilisers 110, 210 on the drill string 60 of FIG. 5, the stabiliser 310 stabilises the drill string, and reams the borehole to a desired diameter, if required.

Turning now to FIG. 8, there is shown a perspective view of a casing shoe 86 having a casing shoe reamer 410 of similar structure to the apparatus 10 of FIGS. 1-4. The casing shoe 86 is also shown in FIGS. 9 and 10, which are views taken in the direction of the arrows G and H shown in FIG. 8. The casing shoe 86 is essentially similar to the drill shoe reamer 80 of FIG. 7. However, the casing shoe 86 is provided lowermost on a string of casing to be run in to a drilled borehole, located in the borehole and cemented in place.

The centraliser 410 serves for centralising the casing within the borehole, and a number of such centralisers 410 are provided spaced along the length of the casing. Also, in a similar fashion to the drill shoe stabiliser 310 of FIG. 7, the casing shoe centraliser 410 (and indeed the further centralisers 410 spaced along the length of the casing) act as a reamer during passage of the casing along the borehole.

The casing shoe 86 includes a jetting nozzle 482 similar to the nozzle 82 of the drill shoe 80, for jetting fluids into the borehole to assist in passage of the casing along the borehole, and the jetting nozzle 482 is drillable to allow subsequent cementation of the casing in the borehole and indeed further downhole procedures.

Turning now to FIG. 11, there is shown a perspective view of a cleaning tool 510. The cleaning tool 510 is also shown in the views of FIGS. 12 and 13, which are taken in the direction of the arrows I and J in FIG. 11, respectively.

The cleaning tool 510 is of similar structure to the apparatus 10 of FIGS. 1-4. However, each rib 520 of the cleaning tool 510 includes a longitudinal recess 88, shown in FIG. 14 and the views of FIGS. 15 and 16, taken in the directions K and L of FIG. 14. The recesses 88 each receive respective cleaning brushes 90, which serve for cleaning an internal wall of a tubing (not shown) in which the cleaning tool is located, by translation and/or rotation of the tool 510 within the tubing. The brushes 90 are releasably secured to the ribs 20 within the recesses 88 and may thus be removed for maintenance and/or replacement, as required. Also, alternative types of cleaning equipment, such as scrapers, wipers, blades or the like may be mounted in the recesses 88, or a combination of such equipment may be provided. Furthermore, alternative tools or equipment may be located in the recesses 88, such as stabiliser arms, elements or shoulders, to facilitate use of the apparatus within boreholes and/or tubing of varying diameters, by provisions of appropriately sized arms.

Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention.

For example, the relevant dimensions of the channel that vary may include a depth and/or length of the channel.

The channel may be formed in or by the main body and may therefore be formed in an outer surface of the body.

At least one of the ribs may be disposed such that the respective rib axis is non-parallel to the rib axis of the other rib, or one or more of the other ribs.

The ribs may be may be provided as integral parts of the main body.

The main axis of each rib and thus corresponding axes of the channels may be disposed non-parallel to a longitudinal axis of the body, that is, inclined relative to the body axis. For example, in embodiments of the invention, the ribs may be helically oriented and thus may extend in a helical direction around the body. This may be of particular utility where it is desired, for example, to promote turbulence in the downhole medium, which may facilitate cleaning and/or transportation of the medium, in particular any entrained solids, to surface.

Ends of the channel may be of greater width relative to a portion or area at a location between the ends in a direction along the length of the channel. However, any other suitable desired arrangement/number of restrictions may be provided in the channel by appropriate shaping thereof.

It may be desired to provide a sharp transition between areas of the rib of differing dimensions if deemed appropriate in view of desired flow characteristics of medium flowing through the channels.

While the invention has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the invention without departing from the spirit or scope of the invention as defined by the appended claims. 

1. A downhole apparatus comprising: a tubular main body; at least one flow channel, the channel extending at least part way along a length of the body and at least one dimension of the channel being non-uniform; and at least one flow guide located adjacent an end of the channel, the flow guide and the channel together defining a flow path for flow of a downhole medium along the body.
 2. The apparatus as claimed in claim 1, wherein the apparatus is dimensioned to be a close fit with tubing or a borehole in which the apparatus is located.
 3. The apparatus as claimed in claim 1, further provided with at least one of a cutting or reaming surface.
 4. The apparatus as claimed in claim 1, wherein the channel is adapted to be bound on one side by an internal wall of tubing or a borehole, such that all or most of the flow of downhole medium past the body is directed along the channel.
 5. The apparatus as claimed in claim 1, wherein the apparatus is a centraliser for centralising a body such as a tubing or tool string within an open hole or within existing downhole tubing.
 6. The apparatus as claimed in claim 1, wherein the apparatus is a stabiliser for stabilising a drill string within an open hole or within existing downhole tubing.
 7. The apparatus as claimed in claim 1, wherein the apparatus is provided as an integral part of a drill pipe.
 8. The apparatus as claimed in claim 1, wherein the apparatus forms part of a shoe.
 9. Apparatus as claimed in claim 8, wherein the apparatus forms part of a casing shoe reamer which includes reaming surfaces for reaming the borehole wall.
 10. Apparatus as claimed in claim 8, wherein the apparatus forms part of a drill shoe reamer which includes reaming surfaces for reaming the borehole wall.
 11. The apparatus as claimed in claim 1, wherein the apparatus is a sleeve of a downhole motor.
 12. The apparatus as claimed in claim 1, wherein the apparatus is a wellbore cleaning tool.
 13. The apparatus as claimed in claim 12, further comprising at least one of a cleaning or abrading blade, brush, scraper, or a wiper.
 14. The apparatus as claimed in claim 1, further comprising a plurality of ribs, each rib upstanding or extending outwardly from an outer surface of the body, and extending at least part way along a length of the body.
 15. The apparatus as claimed in claim 14, wherein the ribs are spaced around a circumference of the main body, and the channel is defined between an adjacent pair of ribs.
 16. The apparatus as claimed in claim 14, further comprising a plurality of channels, each channel defined or bound by an outer surface of the body and side walls of the adjacent ribs.
 17. The apparatus as claimed in claim 16, wherein the side walls of each rib are curved to define a smooth transition between areas of the rib of larger and smaller width.
 18. The apparatus as claimed in claim 14, wherein the ribs have a respective rib main axis, and the ribs are disposed on the body such that the rib main axes are substantially parallel with one another.
 19. The apparatus as claimed in claim 14, wherein each rib has first and second ends of greater width relative to a portion of the rib at a location between said ends.
 20. The apparatus as claimed in claim 14, wherein each rib is elongate and has ends defining lobes with a section extending between the lobes of reduced width.
 21. The apparatus as claimed in claim 14, wherein the ribs define an outer surface adapted to abut an inner wall of a borehole or a tubing in which the apparatus is located.
 22. The apparatus as claimed in claim 1, wherein the channel defines a corresponding channel axis and the flow guide is located on or parallel to the channel axis and is spaced axially along the body relative to the channel.
 23. The apparatus as claimed in claim 1, wherein the flow guide is located such that a downhole medium flowing out of the channel impinges on the flow guide.
 24. The apparatus as claimed in claim 1, wherein the flow guide has a first inward end, relative to the channel, and a second outward end, relative to the channel.
 25. The apparatus as claimed in claim 24, wherein the first, inward end of the flow guide is generally triangular and in a shape of an arrow head.
 26. The apparatus as claimed in claim 1, wherein the channel has first and second axial ends, and the apparatus comprises two flow guides associated with the channel, one located adjacent to the first end of the channel and the other located adjacent the second end.
 27. The apparatus as claimed in claim 1, wherein the apparatus comprises at least two flow guides associated with each channel.
 28. The apparatus as claimed in claim 1, wherein the channel width is non-uniform along a length of the channel.
 29. The apparatus as claimed in claim 1, wherein the channel defines at least one flow restriction where the width of the channel is reduced compared to an adjacent portion or area of the channel.
 30. The apparatus as claimed in claim 29, wherein the at least one flow restriction defines a nozzle which serves, in use, for increasing a velocity of medium flowing therethrough.
 31. The apparatus as claimed in claim 29 wherein the channel defines two such restrictions, one adjacent each end of the channel, with a relatively unrestricted portion at a location between the restrictions in a direction along the length of the channel.
 32. The apparatus as claimed in claim 1, wherein the apparatus comprises a plurality of flow guides spaced around a circumference of the body, adjacent flow guides defining part of a flow path.
 33. The apparatus as claimed in claim 32, wherein the adjacent flow guides define an opening therebetween, which defines an inlet or outlet of one or more flow paths.
 34. The apparatus as claimed in claim 33, wherein the openings are circumferentially spaced or staggered relative to axes of the channels.
 35. The apparatus as claimed in claim 1, wherein the apparatus comprises at least one cutting, abrading or reaming surface for abrading the borehole/tubing wall.
 36. The apparatus as claimed in claim 1, wherein the flow guide is shaped to define a plurality of cutting surfaces, and one or both of first and second ends of the flow guide define a cutting surface.
 37. The apparatus as claimed in claim 36, wherein the apparatus comprises a plurality of flow guides spaced around a circumference of the body, adjacent flow guides defining part of a flow path, wherein the second end of one or both of the flow guides defines a relatively aggressive cutting surface, whilst the first end of one or both of the flow guides define a less aggressive cutting surface.
 38. The apparatus as claimed in claim 37, wherein the second end of the flow guide provided, in use, lowermost on the apparatus defines the relatively aggressive cutting surface.
 39. A downhole apparatus comprising: a tubular main body; and a plurality of elongate ribs upstanding from an outer surface of the main body and extending at least part way along a length thereof, adjacent pairs of ribs defining a flow channel therebetween for flow of a downhole medium along the body; wherein the ribs are shaped such that at least one dimension of each channel is non-uniform and such that respective axes of the channels are disposed substantially parallel to a longitudinal axis of the body.
 40. A downhole apparatus comprising: a tubular main body; at least one flow channel for flow of a downhole medium along the body, the flow channel having a respective flow channel main axis, the channel extending at least part way along a length of the body and at least one dimension of the channel being non-uniform; and at least one flow guide located adjacent an end of the channel and disposed on the flow channel axis.
 41. A downhole tubing shoe comprising: a tubular main body; at least one flow channel for flow of a downhole medium along the body, the channel extending at least part way along a length of the body, at least one dimension of the channel being non-uniform, and an axis of the channel being disposed substantially parallel to a longitudinal axis of the body.
 42. A downhole tubing shoe as claimed in claim 41, wherein the shoe is selected from the group consisting of a casing shoe, a drill shoe and a reamer shoe and a drill shoe reamer. 